Novel plenum window with sonic crystals for indoor noise control

The present study investigates the cognitive performance and subjective perceptions in the context of road traffic noise alone and multiple noises, including construction and ventilation noises. A total of 20 university students were exposed to seven noise conditions. Laboratory experiments employed semantic and episodic memory tasks. Self-reports of perception were collected from the participants. It was found that multiple noise sources impaired the free recall of words, and free recall scores were affected by noise type. Significant differences in free recall scores were found when the noise level difference between the individual noise and multiple noise sources was more than 5 dB. In contrast, word comprehension did not mediate the effects of noise on semantic memory. Annoyance caused by multiple noise sources correlated highly with the results of the free recall and word comprehension tasks. Moreover, loudness and roughness were found to account for the annoyance ratings of combinations of road traffic noise with construction or ventilation noises.

Acoustic panels with different configurations (layered structure with different absorbing materials) are broadly used to attenuate the noise. Multiple panels are preferred due to the presence of multiple air cavities and the repeated reflections which lead to increased sound attenuation. The paper presents an experimental study of sound propagation through multiple panels. A novel design of acoustic panel is proposed by incorporating the sonic crystal in the air cavities of the panel. Sonic crystal (SC) consists of a periodic arrangement of sound hard scatterers which provide the sound reduction in a particular frequency range due to destructive interference in periodic scatterers. The results are based on experimental observations which are supported by the literature. The results show that increasing the number of panels increases the sound insertion loss from the multiple panel structure. However, the panels with air cavity suffer from the sound insertion loss dip, which makes the panel ineffective. The novel acoustic panel (double and triple panel with SC) provides an additional sound reduction due to SC which can be tailored for certain frequency band. For the present case, SC is designed to overcome the insertion loss dip. The novel panel provides an additional insertion loss, reaching a maximum value of 19 and 11 dB, respectively (for the double and triple panel), overcoming the insertion loss dip due to structural vibration.

Recent research suggests that buildings with operable windows in general, and mixed-mode (MM) buildings in particular, can provide improved thermal comfort and control opportunities for users. However, there have been concerns about outdoor noise sources such as traffic or construction noise when windows are opened. Concerns like these may hinder the installation of operable windows in buildings. This article examines 23,000 office building occupants’ perspectives on noise from both sealed and naturally ventilated/MM buildings. The results suggest that occupants near operable windows are more satisfied than those near sealed windows or those far from either window type. Among occupants dissatisfied with noise, complaints about indoor noise sources (such as people talking to each other) are about 10 times more prevalent than outdoor noise complaints.

Sonic crystals are the periodic arrangements of scatterers embedded in a homogeneous material. Their ability to prevent sound wave to propagate in a particular range of frequency demonstrates their use as potential noise barriers. The sonic crystal considered in this work is an array of PVC cylinders (5 × 5) in air bounded by acrylic sheets. This paper studies the sound transmission loss in the sonic crystal by changing the location of the sidewalls. The optimized location of sidewalls of the sonic crystal to get wide band gap and high sound transmission loss has been investigated. To increase the transmission loss, a periodic structure having bi-periodicity, i.e., periodicity in two perpendicular directions is introduced. Both computational (Finite Element simulation) and experimental work has been performed to study the sound transmission loss and the band gaps. To bridge the gap between the two results, an improved finite element model has been proposed with an aim to replicate the experimental situation more closely. Generally, in experiments, insertion loss is calculated while numerically transmission loss is computed, and the two are compared. In this paper, a comparison between insertion loss and transmission loss has also been made numerically, which is compared with the experimental results.

Experimental study of active noise control for a full-scale plenum window in a domestic apartment

This thesis is a contribution towards developing cost-effective ways for reducing outdoor traffic noise in outdoor environments by exploiting the interaction between sound travelling directly to a listener from the source and sound reflected by the intervening ground. Sound propagation over different kinds of porous, rough and mixed impedance ground surfaces have been studied experimentally and numerically. Measurements of short-range acoustic level difference spectra over outdoor ground surfaces and artificially-created surfaces outdoors and in the laboratory have been compared with predictions to establish suitable impedance models. Sound propagation over mixed impedance ground having single or multiple impedance discontinuities has also been studied. Acoustic transmission loss through vegetation, crops and hedges has been investigated. The phenomenon of sound diffraction and periodicity due to rough periodic ground surfaces has been explored through artificially created rough surfaces in the laboratory and outdoors. The phenomenon of surface wave propagation over rough hard surfaces and porous surfaces has been explored through laboratory experiments. Measured data indoors and outdoors have been used to validate numerical (BEM and FEM), empirical and analytical (MST) prediction techniques. The validated numerical methods have been used to make predictions at scales suitable for attenuating traffic noise by means of carefully designed ground treatments. The work has also been extended to railway and tramway noise. It has been found that replacing hard ground with porous ground, introducing single or multiple impedance discontinuities, growing vegetation and introducing low height roughness can all contribute between 3 and 15 dB additional attenuation of traffic noise. In respect of replacing hard ground by porous ground, it is concluded that the ground with lowest flow resistivity i.e. grassland left untouched and allowed to grow wild gives the best attenuation performance. However, dividing a single width of soft ground into alternating strips of hard and soft surfaces does not improve the insertion loss. The overall width of the soft surface is the main factor. Cultivating crops over porous ground can enhance the attenuation but the effect is not very significant for A-weighted levels as most of additional attenuation occurs at higher frequencies above 3 kHz. A 0.3 m high and at least 3 m wide lattice structure design is found to be very useful for traffic noise attenuation since it offers greater insertion loss than the same width and height of parallel low walls and the resulting attenuation is azimuthal angle independent. It has been shown also that the potentially negative effect on insertion loss due to propagation of roughness-induced surface waves over rough surfaces can be reduced by introducing sound absorbing material in between the walls.

Environmental noise pollution (30-8000 Hz, 50-90 dB) has become a central health concern due to its impact on human psychology and physiology. Acoustically, aesthetic architecture has recently been explored for noise control, where sonic crystals (SCs) offer both effective sound attenuation and seamless architectural integration. However, conventional SCs with circular scatterers remain limited in suppressing low-frequency noise because Bragg scattering requires lattice constants comparable to the acoustic wavelength, making large structures impractical for subwavelength regimes. Herein, we propose a Hexa-resonator SC, optimized, simulated, and experimentally validated for its noise attenuation performance. With band structure calculations and eigenfrequency mode analysis, the insertion loss (IL) was investigated over 20-1000 Hz. In the sub-kilohertz region, the SC exhibited two first-order resonance peaks around 150 and 200 Hz and a first-order Bragg band (255-410 Hz). It showed a maximum IL of approximately 36 dB at 303 Hz (in the Bragg region), confirming its effectiveness for low-frequency noise attenuation. The influence of cavity geometry on phase pressure variations and IL was analyzed, revealing hybridization and mode coupling effects. Experiments qualitatively follow the simulated trends.

Acoustic metamaterials (AMMs) have emerged as a promising strategy for low-frequency noise control in ventilation ducts, offering subwavelength, tunable solutions that overcome key limitations of conventional silencers, such as high pressure drop and reduced long-term performance. This review presents a structured analysis of 54 studies on AMMs for duct acoustics, with civil, mechanical, aerospace, and biomedical engineering applications. AMM unit designs are categorized by physical mechanism, including resonant cavities, acoustic membranes, Herschel-Quincke tubes, Fano-like interference structures, duct shape modifications, micro-perforated panels, and porous materials. The associated acoustic and flow-related performance parameters, such as insertion loss, transmission loss, absorption coefficient, flow velocity, temperature, pressure drop, Reynolds number, and Mach number, are systematically examined. Analytical, numerical, and experimental approaches are reviewed with attention to their respective merits and limitations, particularly in capturing multi-physical interactions between acoustics, fluid flow, and structural dynamics. Of the studies surveyed, 35 employed monophysical models, 8 used loosely coupled (monophysical parallel) methods, and only 11 adopted fully coupled multi-physical frameworks. This review highlights the need for integrated design methodologies and standardized evaluation under realistic flow conditions to advance the effective implementation of AMMs in ducted acoustic systems.

Acoustic metamaterials (AMs) have attracted a substantial amount of attention in recent decades where the parameter design plays an important role. However, conventional design methods generally rely on analytical physical models and require a very large number of evaluations of acoustic performance. Here, we propose and experimentally demonstrate an inverse-design method for AMs based on machine learning using a Gauss–Bayesian model. As a result of the cycle of training and prediction and the use of adaptive acquisition functions, this method allows the parameters of AMs to be efficiently designed for specific functionalities without the need for physical models. Considering the significance of low-frequency ventilated sound absorption, we present a design for a typical acoustic metamaterial absorber with multiple structural parameters that facilitate high sound absorption at low frequencies. In the design process, the parameters were adaptively adjusted to improve the sound absorption performance at low frequencies using only 37 evaluations, and this high absorption performance was verified by the agreement of numerical and experimental results. Because of its low cost, high flexibility, and independence from physical models, this method paves the way for tremendous opportunities in the design of various AMs for particular desired functionalities.

BackgroundRoad traffic noise has been associated with adverse health effects including sleep disturbances. Use of sleep medication as an indicator of sleeping problems has rarely been explored in studies of the effects of traffic noise. Furthermore, using registry data on sleep medications provides an opportunity to study the effects of noise on sleep where attribution of sleep problems to noise is not possible.MethodsWe used questionnaire data from the population-based study Health and Environment in Oslo (HELMILO) (2009–10) (n = 13,019). Individual data on sleep medications was obtained from the Norwegian Prescription Database (NorPD). Noise levels (Lnight) were modeled for the most exposed façade of the building at each participant’s home address. Logistic regression models adjusted for potential confounders were used to analyze the association between traffic noise and sleep medication use both for one whole year and for the summer season. The results were reported as changes in the effect estimate per 5 decibel (dB) increase in noise level.ResultsWe observed no association between traffic noise and sleep medication use during one year [odds ratio (OR) = 1.00; 95% confidence interval (CI): 0.96, 1.04]. For sleep medication use in the summer season, there was a positive, however non-significant association (OR = 1.04; 95% CI: 0.99, 1.10). Among individuals sleeping with the bedroom window open, the association increased slightly and was borderline statistically significant (OR = 1.06; 95% CI: 1.00, 1.12).ConclusionsWe found no evidence of an association between traffic noise and sleep medication use during one year. However, for the summer season, there was some suggestive evidence of an association. These findings indicate that season may play a role in the association between traffic noise and sleep, possibly because indoor traffic noise levels are likely to be higher during summer due to more frequent window opening. More studies are, however, necessary in order to confirm this.

Effects of reference microphone position on active sound reduction across an acoustic plenum window

Urban noise pollution attracts global concern since it seriously affects and harms human health and activities. Noise-induced annoyance is one of the salient noise effects on human perception. As an efficient noise reduction tools, noise masking scheme is employed to reduce noise-induced annoyance. Both music and water sounds are commonly used sound maskers in noise masking where music sound masking is seldom discussed for urban noise. In this study, we conduct a subjective listening test to evaluate the masking capability of music and water sounds for Singapore urban noise. The results show that masking is a good solution in mid-to-high annoyance scenario for traffic and construction noise. And music sound presents similar performance in reducing the annoyance to that of the water sounds.

A tunable negative modulus metamaterial is presented, and it is achieved by adjusting the medium density and an effective volume of a split hollow sphere (SHS). This work comprises experimental and numerical studies. The effects of water/air component and the steel ball on the transmission properties were investigated in the impedance tube system. The experimental results show that the transmission dip has a significant blue-shift with increasing water content, whereas the steel ball has a relatively small influence on the resonant frequency. The simulated results by the finite-element method (FEM) are in agreement with the experimental results. Based on medium parameters among the SHS, acoustic metamaterial (AM) with negative modulus can easily be designed in the expected frequency domain, and it provides a convenient route to tune AMs.

Approval of major infrastructure projects in Australia is contingent on a vigorous environmental assessment process demonstrating that the impacts from such proposals are acceptable and can be satisfactorily managed. As part of this process, an assessment of construction noise is undertaken by predicting the level and duration of impact. Given the scale, complexity and programs for delivery of major infrastructure projects such as the Sydney Metro, the approach to assessment of environmental impacts is typically undertaken based on early concept designs, and assumptions which enable potential worst-case impacts to be considered. Ongoing design development and construction methodologies continue to occur, and are finalised by the contractor responsible for delivering the package of works for the project. Layers of conservatism could therefore be built into the process to ensure that environmental impacts are understood, and appropriate mitigation measures are considered. Moreover, common predictive noise modelling tools are believed to under-estimate the level of barrier insertion loss provided by residential buildings in urban scenarios, further exacerbating the over-prediction of construction noise impacts. By use of case studies, the present paper examines the challenges of assessing and managing construction noise associated with a major infrastructure project in Sydney, Australia.

Sonic crystal structures consisting of periodically-arranged solid vertical cylinders can act as sound barriers at certain frequencies. Their performance depends on the filling fraction which is determined by the spacing and cylinder radius. To be effective the filling fraction must be high. This means that periodic arrays with relatively low filling fractions such as in trees belts are not effective as traffic noise barriers. The effects of partially perturbing the positions of sonic crystal elements have been investigated by modelling and laboratory measurements and have been shown to improve the insertion loss of the periodic structure. It is argued that partial perturbation of regular tree planting near highways will improve their noise attenuation. Furthermore, much previous research assumes the sonic crystal structure to be in the free field, i.e. no account has been taken of the presence of the ground surface. With a conventional, wall type, barrier the ground effect is reduced by presence of the b...